The dCap protocol allows to check whether a dataset is on tape only or has a copy on a dCache disk. The dCap library API call is int dc_check(const char *path, const char *location) and the dccp options are -t -1 -P. For a full list of dCap library API calls and dccp options, please refer to to http://www.dcache.org/manuals/libdcap.shtml and http://www.dcache.org/manuals/dccp.shtml respectively. Using a standard dCache installation those calls will return a guess on the file location only. It is neither checked whether the file is really on that pool or if the pool is up. To get a strict checking a dCap door has to be started with a special (-check=strict) option.

#
#    dCap    D o o r
#
create dmg.cells.services.login.LoginManager DCap-strict \
            "${specialDCapPort} \
             diskCacheV111.doors.DCapDoor \
             -check=strict \
             -export \
             -prot=telnet -localOk \
             -maxLogin=1500 \
             -brokerUpdateTime=120 \
             -protocolFamily=dcap \
             -loginBroker=LoginBroker"

This door will do a precise checking (-check=strict). To get the dCap lib and dccp to use this door only, the DCACHE_DOOR environment variable has to be set to doorHost:specialDCapPort in the shell, dccp is going to be used. In the following example we assume that the specialDCapPort has been set to 23126 :

[user] $ export DCACHE_DOOR=dcachedoorhost:23126
[user] $ dccp -P -t -1 /pnfs/domain.tv/data/cms/users/waste.txt

If dccp returns File is not cached and this dCache instance is connected to an HSM, the file is no longer on one of the dCache pools but is assumed to have a copy within the HSM. If the dccp returns this message and no HSM is attached, the file is either on a pool which is currently down or the file is lost.